Pulmonary Function and Symptom Responses after 6.6-Hour Exposure to 0.12 ppm Ozone with Moderate Exercise

Abstract

Episodes occasionally occur when ambient ozone (O₃) levels remain at or near 0.12 ppm for more than 6 h. Small decrements In lung function have been reported following 2-h exposures to 0.12 ppm O₃. For short exposures to higher O₃ concentrations, lung function decrements are a function of exposure duration. Thus, we investigated the hypothesis that prolonged exposure to 0.12 ppm O₃ would result in progressively larger changes in respiratory function and symptoms over time. Ten nonsmoking males (18-33 yr) were exposed once to clean air and once to 0.12 ppm O₃ for 6.6 h. Exposures consisted of six 50-min exercise periods, each followed by 10-min rest and measurement; a 35-min lunch period followed the third exercise period. Exercise ventilation averaged approximately 40 L/min. Forced expiratory and inspiratory spirometry and respiratory symptoms were measured prior to exposure and after each exercise. Airway reactivity to methachollne was determined after each exposure. After correcting for the air exposures, FEV1.0 was found to decrease linearly during the O₃ exposure and was decreased by an average of 13.0 percent (591 mL) at the end of exposure. Decreases in FVC and FEF25-75 % were also linear and averaged 8.3 and 17.4 percent, respectively, at the end of exposure. On forced Inspiratory tests, the FIVC and FIV05 were decreased 12.6 and 20.7 percent, respectively. Increases in the symptom ratings of cough and pain on deep Inspiration were observed with O₃ exposure but not with clean air. Airway reactivity to methacholine was approximately doubled following O₃ exposure. We conclude that prolonged exposure to 0.12 ppm O₃ results in progressive changes in respiratory function, a marked increase in nonspecific airway reactivity, and progressive changes in symptoms.